Electric motors employing a combination of electromagnets and permanent magnets for the purposes identified in the preceding paragraph are disclosed in a number of previously issued U.S. patents. Those of which I am aware are Nos.:
673,980 issued May 14, 1901, to Engelhardt for ELECTROMAGNET MOTOR;
722,042 issued Mar. 3, 1903, to Poly Aguirre for ELECTROMAGNETIC MOTOR;
1,907,221 issued May 2, 1933, to Smulski for ELECTRIC MOTOR;
1,992,137 issued Feb. 19, 1935, to Zeininger for ELECTRIC MOTOR;
2,281,081 issued Apr. 28, 1942, to Sheldon for ELECTROMAGNET MOTOR;
2,404,331 issued July 16, 1946, to Werner for ELECTROMAGNETIC MOTOR;
2,374,998 issued May 1, 1945, to Hitchcock for PERMANENT MAGNET ELECTRIC MOTORS;
2,864,018 issued Dec. 9, 1958, to Aeschmann for IMPULSE MOTOR;
2,922,943 issued Jan. 26, 1960, to Rupp for ELECTRIC MACHINE;
2,968,755 issued Jan. 17, 1961, to Baermann for MAGNETIC MOTOR
3,072,812 issued Jan. 8, 1963, to Gaddes for PERMANENT MAGNET MOTOR;
3,331,973 issued July 18, 1967, to McClure for MAGNETIC MOTOR;
3,670,189 issued June 13, 1972, to Monroe for GATED PERMANENT MAGNET MOTOR;
4,025,807 issued May 24, 1977, to Clover et al. for ELECTROMAGNETIC MOTOR;
4,305,024 issued Dec. 8, 1981, to Kuroki for MAGNETIC MOTOR;
4,357,551 issued Nov. 2, 1982, to Dulondel for D.C. IMPULSION MOTOR;
4,361,790 issued Nov. 30, 1982, to Laesser et al. for ELECTROMAGNETIC MOTOR ROTATABLE IN EITHER DIRECTION;
4,564,778 issued Jan. 14, 1986, to Yoshida for DC BRUSHLESS ELECTROMAGNETIC ROTARY MACHINE;
A major disadvantage of the prior art of permanent magnet motors is that they are unable to vary the amount of rotational power required. As a result, the size, and therefore power usage, of a motor is determined by the amount of energy required to perform the work at the moment of heaviest load. Therefore, energy is wasted at all times other than at the moment of heaviest load.
Also, permanent magnet type motors have been plagued by a low starting torque. Another common disadvantage of existing permanent magnet motors is the difficulty of stopping the rotor of the motor in a precise position with respect to the stator. Additionally, existing permanent magnet motors have not been designed to enable the rotor to be locked in a fixed position relative to the stator, without using a rachet or other relatively quick wearing mechanical device (see the discussion in Aeschmann U.S. Pat. No. 2,864,018).
Another important disadvantage of many existing permanent magnet motors is the make-and-break type mechanical switching which is employed to energize the electromagnets of the motor in the sequence needed to cause the armature of the motor to rotate. These switching devices generate sparks, and motors employing them consequently cannot be used in flammable or explosive environments unless the motor is encased in an expensive explosion proof housing, which makes their use impractical in many circumstances. See examples of such mechanical switching devices disclosed in Sheldon U.S. Pat. No. 2,281,081; Hitchcock U.S. Pat. No. 2,374,998; Rupp U.S. Pat. No. 2,922,943; Baermann U.S. Pat. No. 2,968,755; and McClure U.S. Pat. No. 3,331,973.